(1) Field of the Invention
This invention relates to an ultraviolet irradiating apparatus for emitting ultraviolet light toward a work piece such as a semiconductor wafer or electronic part and a frame holding the work piece through an ultraviolet sensitive adhesive tape applied to the back surface of the work piece.
(2) Description of the Related Art
In a conventional process of manufacturing semiconductor wafers (hereinafter simply called “wafers”) or electronic parts, work pieces are processed as held with an ultraviolet sensitive adhesive tape applied thereto.
The semiconductor manufacturing process includes a dicing step for cutting a wafer into chips, for example. In this dicing step, the wafer is mounted centrally of a ring-shaped frame, and held (supported) with an ultraviolet sensitive adhesive tape applied to the back surface of the wafer in a way to cover the ring-shaped frame as well.
That is, a semiconductor wafer fixed to a wafer support structure is cut by a cutter, leaving the adhesive tape adhering to the wafer, to avoid fragmenting and scattering of chips. Further, an ultraviolet sensitive adhesive tape is used because it has strong adhesion for withstanding impacts occurring in time of cutting, and in order to allow cut chips to separate easily from the adhesive tape in a die-bonding step following the dicing step. That is, the adhesive strength of this tape is lowered when irradiated by ultraviolet light, and this property of the tape is utilized.
In a specific example of ultraviolet irradiating apparatus, a work piece is enclosed in a cover, and an inert gas is fed into its interior. A predetermined quantity of ultraviolet light is emitted by opening and closing a shutter disposed between an ultraviolet lamp and the wafer (see Japanese Unexamined Patent Publication No. 6-204335).
However, the apparatus using the conventional ultraviolet irradiating method has the following drawbacks.
To meet the high-density packaging requirement today, a thinning process using wafers of large diameter (e.g. 300 mm) tends to result in an ever lessening strength of the wafers. Furthermore, due to the heat generated in time of ultraviolet irradiation, the adhesive tape tends to soften and become slack under the weight of such a large wafer. Consequently, there has arisen a problem of corners of adjoining diced chips rubbing against one another to be damaged.
When intervals between the chips or packages are reduced by slackening of the adhesive tape, an operating inconvenience will occur where, for example, individual chips cannot be recognized accurately in picking up the chips with a suction collet.
Moreover, the adhesive tape which has once slackened by heat cannot be restored. While a wafer with the adhesive tape in the slack state is transported to the bonding step, the chips could contact each other to be damaged. When sucking chips from a wafer joined with a ring-shaped frame with a suction collet for transport, the collet may fail to suck the chips accurately, thereby damaging the chips.